As a method of estimating the three-dimensional position of an object from images, a twin-lens stereo method is available. A twin-lens stereo method estimates the distance to a target object, on the basis of the principle of triangulation, from images that have been respectively captured by two cameras arranged parallel to each other, the positional relationship of the cameras being known, by using a displacement (disparity), in terms of pixels, of a single object (target object) between the images. In the twin-lens stereo method, it is difficult to synchronize the timings of acquiring images between cameras. When an image of a moving target object is captured, the disparity changes and accurate estimation of the distance to the target object is impossible, which has been an issue. To address such an issue, Shimizu and Fujiyoshi (Chubu University), “Fukusu Hidouki Kamera wo Mochiita Kosoku Sanjigen Ichi Suitei ni Kansuru Kenkyu (Study on high-speed three-dimensional position estimation using multiple asynchronous cameras)”, 2005 discloses a technique in which a corresponding point in a frame that does not exist is created imaginarily and the corresponding imaginary point that has been created and an observed point are used to estimate the three-dimensional position of a target object.